Methods and systems for providing control stability in a vacuum generation system using an override proportional-integral-derivative (pid) controller

ABSTRACT

Certain embodiments provide a vacuum generation system with an override PID controller, a proportional valve, and a vacuum generator. The override PID controller allows the vacuum generation system to control the operating range of supply air pressure that is provided to the vacuum generator. By controlling the operating range of the supply air pressure, the vacuum generation system is able to avoid entering the decreasing or non-monotonic region of the vacuum generator.

PRIORITY CLAIM

This application claims the benefit of priority of U.S. ProvisionalPatent Application Ser. No. 63/077,757 titled “METHODS AND SYSTEMS FORPROVIDING CONTROL STABILITY IN A VACUUM GENERATION SYSTEM USING ANOVERRIDE PROPORTIONAL-INTEGRAL-DERIVATIVE (PID) CONTROLLER”, filed onSep. 14, 2020, whose inventors are Brian T. Chiem, which is herebyincorporated by reference in its entirety as though fully and completelyset forth herein.

TECHNICAL FIELD

The present disclosure relates generally to methods and systems forproviding control stability in a vacuum generation system using anoverride proportional-integral-derivative (PID) controller.

BACKGROUND

During small incision surgery, and particularly during ophthalmicsurgery, small probes are inserted into the operative site to cut,remove, or otherwise manipulate tissue. During these surgicalprocedures, fluid and tissue may be aspirated from the surgical site.

Examples of ophthalmic surgeries during which fluid and tissue areaspirated include vitreo-retinal procedures. Vitreo-retinal proceduresmay include a variety of surgical procedures performed to restore,preserve, and enhance vision. Vitreo-retinal procedures may beappropriate to treat many serious conditions of the back of the eye.Vitreo-retinal procedures may treat conditions such as age-relatedmacular degeneration (AMD), diabetic retinopathy and diabetic vitreoushemorrhage, macular hole, retinal detachment, epiretinal membrane, CMVretinitis, and many other ophthalmic conditions. In order to treatcertain conditions in the back of the eye, a surgeon may first performvitrectomy, as part of the vitreo-retinal procedure that is beingperformed. Vitrectomy refers to a surgical removal of the vitreous,which is a normally clear, gel-like substance that fills the center ofthe eye. The vitreous may make up approximately two-thirds of the eye'svolume, giving it form and shape before birth.

Removal of vitreous can involve a vitrector (also referred to as the“cutter” or “vitreous cutter”). In some examples, the vitrector may bepowered by a pneumatic vitrectomy machine (e.g., surgical console)including one or more pneumatic valves (also referred to as drivevalves). In such examples, the vitrector may work like a tinyguillotine, with an oscillating microscopic cutter to remove thevitreous gel in a controlled fashion. In some other examples, thevitrector may cut the vitreous using laser light or some othertechnology such as ultrasound. In addition to cutting the vitreous, thecutter may also be configured to aspirate the surgically cut vitreous.Aspiration may be provided by a vacuum generator (e.g., Venturi vacuum)that is coupled to the cutter through a tube that provides an aspirationchannel.

Other examples of ophthalmic surgeries during which fluid and tissue areaspirated include phacoemulsification, which refers to a cataractoperation in which a diseased lens is emulsified and aspirated out ofthe lens capsule. In some examples, the phacoemulsification probe maybreak up the lens by ultrasound (or other technologies, such as laserlight, etc.). For aspirating the broken up lens, the phacoemulsificationprobe may be powered by a vacuum generator (e.g., Venturi vacuum) thatis coupled to the phacoemulsification probe through a tube that providesan aspiration channel.

Certain existing vacuum generators, such as certain existing Venturivacuum generators, operate using compressed air to flow through orificesthat generate vacuum pressure. However, a common property of thesevacuum generators is that beyond a certain amount of supply pressure,the vacuum generator becomes less efficient and generates less vacuumpressure as supply pressure increases. For example, vacuum pressureincreases as the supply air pressure increases in the range of 0-60 psig(pounds per square inch gauge). However, vacuum pressure begins todecrease as the supply air pressure increases in the range of 60-87psig. More specifically, when the supply air pressure reaches around,for example, 60 psig and higher, vacuum pressure starts decreasing,thereby causing a standard PID controller, which is used to regulate thesupply air pressure, to drive to instability. In such an example, whenthe supply air pressure is in the range of 0-60 psig, the vacuumgenerator may be referred to as operating in a monotonic region. On theother hand, when the supply air pressure is above, for example, 60 psig,the vacuum generator may be referred to as operating in a non-monotonicor decreasing region. While 60 psig is used in the above example, it isto be understood that other supply air pressure values are alsocontemplated.

BRIEF SUMMARY

The present disclosure relates generally to methods and systems forproviding control stability in a vacuum generation system using anoverride proportional-integral-derivative (PID) controller.

Certain embodiments provide a method of controlling vacuum pressure in avacuum generation system. The method comprises receiving a vacuumpressure sensor reading from a vacuum pressure sensor. The methodfurther comprises calculating a first error between the vacuum pressuresensor reading and a vacuum pressure set point. The method furthercomprises calculating a first voltage level for controlling aproportional valve based on the first error. The method furthercomprises receiving a supply air pressure sensor reading from a supplyair pressure sensor. The method further comprises calculating a seconderror between the supply air pressure sensor reading and the supply airpressure set point. The method further comprises calculating a secondvoltage level for controlling a proportional valve based on the seconderror. The method further comprises determining the lower of the firstand second voltage levels. The method further comprises providing thelower voltage level to the proportional valve. The method furthercomprises causing, using the proportional valve, supply air pressure tobe provided to a vacuum generator based on the lower voltage level. Themethod further comprises providing, using the vacuum generator, vacuumpressure based on the supply air pressure to a surgical tool.

Certain embodiments provide a vacuum generation system. The vacuumgeneration system comprises a first proportional-integral-derivative(PID) controller, configured to receive a first error between a vacuumpressure sensor reading associated with a vacuum generator and a vacuumpressure set point, and calculate a first voltage level for controllinga proportional valve based on the first error. The vacuum generationsystem further comprises a second PID controller, configured to receivea second error between a supply air pressure sensor reading and thesupply air pressure set point, and calculate a second voltage levelbased on the second error. The vacuum generation system comprisesdetermining the lower of the first and second voltage levels. The vacuumgeneration system further comprises the proportional valve, configuredto receive the lower voltage level, and cause supply air pressure to beprovided to a vacuum generator based on the voltage level. The vacuumgeneration system further comprises the vacuum generator, configured toprovide vacuum pressure based on the supply air pressure to a surgicaltool.

Certain embodiments provide a vacuum generation system comprising amemory comprising executable instructions and a processor in datacommunication with memory and configured to execute the instructions,which configures the processor to: receive a first error between avacuum pressure sensor reading associated with a vacuum generator and avacuum pressure set point; calculate a first voltage level based on thefirst error; receive a second error between a supply air pressure sensorreading and the supply air pressure set point; calculate a secondvoltage level based on the second error; determine the lower of thefirst and second voltage levels and provide the lower voltage level tothe proportional valve. The vacuum generation system further comprisesthe proportional valve, configured to cause supply air pressure to beprovided to a vacuum generator based on the lower voltage level. Thevacuum generation system further comprising the vacuum generatorconfigured to provide vacuum pressure based on the supply air pressureto a surgical tool.

The following description and the related drawings set forth in detailcertain illustrative features of one or more embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings depict only examples of certain embodiments of thepresent disclosure and are therefore not to be considered as limitingthe scope of this disclosure.

FIG. 1 illustrates an example surgical console, in accordance withcertain embodiments.

FIG. 2 illustrates an example vitrectomy probe, in accordance withcertain embodiments.

FIG. 3 illustrates a side vide of the vitrectomy probe of FIG. 2, inaccordance with certain embodiments.

FIG. 4 illustrates an example cutting mechanism of the vitrectomy probeof FIG. 2, in accordance with certain embodiments.

FIG. 5 illustrates an example phacoemulsification probe, in accordancewith certain embodiments.

FIG. 6 illustrates a prior art vacuum generation system, in accordancewith certain embodiments.

FIG. 7 illustrates a vacuum generation performance graph associated withthe prior art vacuum generation system of FIG. 6, in accordance withcertain embodiments.

FIG. 8 illustrates an example schematic vacuum generation system with anoverride PID controller, in accordance with certain embodiments.

FIG. 9 illustrates an example schematic vacuum generation system with anoverride PID controller, in accordance with certain embodiments.

FIG. 10 illustrates example operations of the vacuum generation systemof FIG. 8, in accordance with certain embodiments.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe drawings. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

While features of the present disclosure may be discussed relative tocertain embodiments and figures below, all embodiments of the presentdisclosure can include one or more of the advantageous featuresdiscussed herein. In other words, while one or more embodiments may bediscussed as having certain advantageous features, one or more of suchfeatures may also be used in accordance with various other embodimentsdiscussed herein. In similar fashion, while exemplary embodiments may bediscussed below as device, instrument, or method embodiments it shouldbe understood that such exemplary embodiments can be implemented invarious devices, instruments, and methods.

FIG. 1 illustrates an example of a surgical console 101, according tocertain embodiments. Surgical console 101 may be configured to drive oneor more tools 103, which may include vitrectors, phacoemulsificationprobes, and other tools with aspiration functionality. In operation,surgical console 101 may function to assist a surgeon in performingvarious ophthalmic surgical procedures, such as vitrectomy,phacoemulsification, and similar procedures. In embodiments where tool103 is a vitrector, surgical console 101 includes one or more modules orcomponents to power the vitrector for the purpose of cutting thevitreous. For example, in certain embodiments, surgical console 101 mayinclude a pneumatic module that uses compressed gas, such as nitrogen,to power the vitrector. In certain other embodiments, surgical console101 may include a laser source for generating laser light that is usedby the vitrector to cut the vitreous. In embodiments where tool 103 is aphacoemulsification probe, surgical console 101 includes one or moremodules or components to power the phacoemulsification probe to emulsifythe lens during cataract surgery.

The surgical console 101 may include a display 109 for displayinginformation to a user (the display may also incorporate a touchscreenfor receiving user input). The surgical console 101 may also include avacuum generator that is coupled to a port 107. Tool 103 is operativelycoupled to the vacuum generator through a line 105 that connects to port107. The vacuum generator creates vacuum at the tip of tool 103, whichcauses the surgically cut or emulsified material or tissue to bevacuumed into tool 103 and transported along line 105 to surgicalconsole 101. Note that line 105 may be representative of a number oftubes that may couple tool 103 with surgical console 101. For example,line 105 may be representative of a pneumatic line or an optical fibercable for powering tool 103 for cutting purposes as well as anaspiration or vacuum line for transporting the aspirated material backto surgical console 101.

FIGS. 2 and 3 illustrate a perspective view and a side view of anexemplary vitrector 203, respectively, according to certain embodimentsdescribed herein. FIGS. 2 and 3, therefore, are described together forclarity. Vitrector 203 is an example of tool 103. As depicted in FIGS.2-3, vitrector 203 comprises a probe 210 and a base unit 220. Probe 210is partially and longitudinally disposed through a distal end 221 ofbase unit 220 and may be directly or indirectly attached thereto withinan interior chamber of base unit 220. Probe 210 may be inserted into aneye for performing vitrectomy. Note that, as described herein, a distalend or portion of a component refers to the end or the portion that iscloser to a patient's body during use thereof. On the other hand, aproximal end or portion of the component refers to the end or theportion that is distanced further away from the patient's body.

Base unit 220 further provides a port 223 at a proximal end 225 thereoffor one or more supply lines to be routed into an interior chamber ofthe base unit 220. In certain embodiments, port 223 may berepresentative of two or more ports. In certain embodiments, port 223may provide a connection between the base unit 220 and a tube or vacuumline (e.g., line 105 of FIG. 1) of a vacuum generator (e.g., a vacuumgenerator in surgical console 101) for aspiration. In certainembodiments, port 223 may provide a connection to an optical fiber cablethat couples to one or more laser light sources (e.g., in surgicalconsole 101) for providing laser light that is used by vitrector 203 forcutting the vitreous. In certain embodiments, port 223 may provide aconnection to pneumatic line that that couples a pneumatic module (e.g.,in surgical console 101) that uses compressed gas, such as nitrogen, topower vitrector 203 for cutting the vitreous. Note the vitrector 203 maybe powered using other technologies, as one of ordinary skill in the artappreciates. As further described in relation to FIG. 4, vitrector 203comprises a cutting port 216 at the distal portion of probe 210. Incertain embodiments, vitrector 203 is able to cut and aspirate thevitreous through this port 216.

FIG. 4 illustrates an example of a cutting mechanism used in conjunctionwith vitrector 203 of FIGS. 2 and 3. More specifically, FIG. 4illustrates the distal end of probe 210 of vitrector 203, the distal endprobe 210 housing a probe cutter 425 that acts as a cutting device.Probe cutter 425 reciprocates inside probe 210. In certain embodiments,probe cutter 425 is a hollow tube with a sharpened tip. In certainembodiments, probe cutter 425 comprises a cutter port that is similar toand interacts with cutter port 216 of probe cutter 425 to increase thecutting efficiency and effectiveness. As the probe cutter 425 moves backand forth, the probe cutter 425 alternately opens and closes cutter port216 with the sharpened tip of probe cutter 425. Each cycle of the probecutter 425 through the distal end of probe 210 may cut through materialsuch as vitreous in the cutter port 216 as the probe cutter 425 isclosing. The surgically cut vitreous is then aspirated through probe210. In certain embodiments, the surgically cut vitreous is aspiratedfrom the circular area between the outer surface of probe cutter 425 andthe inner surface of probe 210. In certain embodiments, the surgicallycut vitreous is, in addition or instead, aspirated through probe cutter425 (e.g., through the hollow compartment thereof).

Note that FIGS. 2-3 illustrate only one example of a vitrector. Also,FIG. 4 only illustrates only one example of a cutting mechanism that maybe used as part of a vitrector. As described above, laser light or othermechanism may instead be used. Further, tool 103 may be aphacoemulsification probe, such as the one shown in FIG. 5.

FIG. 5 illustrates an example phacoemulsification probe 503 including ahandpiece body 520 and probe 510 that may be inserted into an eye forperforming phacoemulsification. A cutting tip 516 extends beyond thedistal end of probe 510. Cutting tip 516 is a hollow cylindrical tube orshaft that propagates ultrasound waves provided by an ultrasound powerline 524. The ultrasound waves emulsify the lens. Cutting tip 516 alsoprovides an aspiration port 518 through which the emulsified lens isaspirated as a result of the vacuum pressure provided by an aspirationline 523. Probe 510 also has an irrigation port for irrigating the lensduring the phacoemulsification process. Note that FIG. 5 illustratesonly one example of a phacoemulsification probe. Also, FIG. 5 onlyillustrates one example of an emulsification mechanism that may be usedas part of a phacoemulsification probe.

As described above, certain existing vacuum generators, that may be usedto enable a tool 103 (e.g., vitrector 203, phacoemulsification probe503, etc.) to aspirate material from a surgical site (e.g., a patient'seye), operate using compressed air to flow through orifices thatgenerate vacuum pressure. However, a common property of these vacuumgenerators is that beyond a certain amount of supply air pressure, thevacuum generator becomes less efficient and generates less vacuumpressure as supply air pressure increases. FIG. 6 illustrate examplesoperations of these vacuum generators.

FIG. 6 illustrates a high-level diagram that illustrates operations ofan example prior art vacuum generation system 600. As shown, vacuumgeneration system 600 comprises a vacuum generator 650, such as aVenturi vacuum, that generates vacuum pressure. As described above,vacuum generation system 600 may be positioned in a surgical console(e.g., surgical console 101) that couples to tool 103. As such, thevacuum pressure that is provided by vacuum generation system 600 may beused for the aspiration procedures described above. Vacuum generationsystem 600 also includes a proportional valve 652. Vacuum generator 650takes as input supply air, whose pressure (i.e., supply air pressure651) is set by proportional valve 652, and creates vacuum with a certainvacuum pressure 657. In certain embodiments, vacuum generator 650 is aVenturi vacuum generator that creates vacuum by a pump with supply airrunning through the pump. One of ordinary skill in the art appreciatesthe inner-workings of a Venturi vacuum generator, and, therefore,details relating to such inner-workings are not described herein forbrevity.

As described above, proportional valve 652 sets the supply air pressure651 for the supply air that is provided to vacuum generator 650. Aproportional valve provides a change in output pressure or flow in thesame ratio as the change in the input. For example, if the input doublesthen the output will also double. In FIG. 6, proportional valve 625 isoperatively coupled to an air compressor or air source reservoir 658.Proportional valve 625 takes as input compressed air and regulates thepressure (by providing less or more air) based on the input voltage 653that is provided to proportional valve 652. The higher the voltage 653the higher the supply air pressure 651. Vacuum generation system 600further comprises a PID controller 654, which is used to control vacuumpressure 657. Generally, a PID controller provides calculations fordriving an actuator (e.g., proportional valve 652) based on an amount oferror (calculated as the difference between the desired set point andthe last sensor reading), integral, and derivative of the error trend.

To illustrate the operations of PID controller 654 with a simpleexample, PID controller 654 takes as input an error value thatcorresponds to the difference between the current vacuum pressure and avacuum pressure set point 656. PID controller 654 then computes both thederivative and the integral of this error value with respect to time.Based on such a computation, PID controller 654 then provides an output(e.g., in the form of a voltage value). The output may be calculated indifferent ways, as one of ordinary skill in the art appreciates. In oneexample, the output may be equal to the proportional gain (K_(P)) timesthe magnitude of the error plus the integral gain (K_(i)) times theintegral of the error plus the derivative gain (K_(d)) times thederivative of the error.

Vacuum pressure set point 656 refers to a certain vacuum pressure thatmay be desired by the user of a corresponding tool 103 (e.g., vitrector203, phacoemulsification probe 503, etc.). The user may change thevacuum pressure set point 656 by providing input to surgical console 101through a graphical user-interface displayed on display 109 of surgicalconsole 101, a foot pedal of surgical console 101, or through some othermechanism. The current vacuum pressure refers to the last sensor readingof the vacuum pressure that is provided to PID controller 654 by avacuum pressure sensor 659. For example, vacuum pressure sensor 659 mayperiodically or continuously sense the current vacuum pressure.

PID controller 654, therefore, periodically or continuously calculatesthe amount of voltage 653 that should be provided to proportional valve652 (e.g., using a driver circuit) to help vacuum generation system 600ultimately achieve the vacuum pressure set point 656. As describedabove, the higher the voltage 653 the higher the supply air pressure 651and, therefore, the higher the vacuum pressure 657. As such, bycontrolling the voltage 653 based on the error calculated by the PIDcontroller 654, vacuum generation system 600 is able to control thevacuum pressure 657.

However, in vacuum generation system 600, beyond a certain amount ofsupply air pressure 651, vacuum generator 650 becomes less efficient andgenerates less vacuum pressure 657 as supply air pressure increases 651.

FIG. 7 illustrates a vacuum generation performance graph 700 of a priorart vacuum generation system, such as vacuum generation system 600. Asshown in graph 700, the vacuum pressure (measured in mmHg, which refersto a millimeter of mercury) increases as the supply air pressureincreases in the range of 0 to a certain threshold (e.g., 60 psig(pounds per square inch gauge)). However, the vacuum pressure begins todecrease as the supply air pressure increases above the threshold. Forexample, when the supply air pressure reaches around 60 psig andincrease, vacuum pressure starts decreasing, thereby causing a standardPID controller (e.g., PID controller 654) to drive to instability. Notethat 60 psig is an example and different vacuum generators may havedifferent thresholds. For example, the supply air pressure set point maybe approximately in a range of 40 to 60 psig.

Using a single PID controller, such as in the manner described inrelation to vacuum generation system 600, therefore, causes vacuumgeneration system 600 to become unstable if the system reaches thedecreasing or non-monotonic region (e.g., 60-87 psig). For example, insuch situations, PID controller 654 senses that the vacuum pressure 657is lower than the vacuum pressure set point 656, which causes PIDcontroller 654 to increase voltage 653. The increased voltage opensproportional valve 652 even more, allowing more supply air (i.e., highersupply air pressure 651), which causes vacuum generator 650 to decreasevacuum pressure 657 even more. The additional reduction in vacuumpressure 657 causes PID controller 654 to increase voltage 653 again,and the cycle repeats. In such a situation, vacuum generation system 600is driven to its limits and becomes unstable. To recover from thisinstability, vacuum pressure set point 656 must be reduced to be lowerthan the current vacuum pressure 657, which causes PID controller 654 todecrease voltage 653 until vacuum generation system 600 is back in themonotonic region (e.g., 0-60 psig of supply air pressure). As such,vacuum generation system 600 may experience an initial increase and thena decrease of the vacuum pressure until vacuum pressure set point 656 isreached. As a result, vacuum generation system 600 may experience asluggish or slow performance in reaching a desired vacuum pressure setpoint, in the situations described above.

Accordingly, certain embodiments described herein relate to a vacuumgeneration system with a first PID controller and a second override PIDcontroller, respectively, corresponding to a first feedback loop and asecond feedback loop parallel with the first feedback loop. The firstPID controller is configured to make calculations based on an errorbetween the current vacuum pressure and the vacuum pressure set pointwhile the second, override PID controller is configured to makecalculations based on an error between the current supply air pressureand a supply air pressure set point. The calculations made by the firstand second feedback loops are then compared to determine a lower orminimum voltage to be used to drive the vacuum generation system.

FIG. 8 illustrates a high-level diagram that illustrates exampleoperations of a vacuum generation system 800, in accordance with certainembodiments. As shown, vacuum generation system 800 includes a firstfeedback loop 810 having a first PID controller 868 that is configuredto take as input a first loop vacuum pressure error (“first loop error”)880, which corresponds to the difference between the current vacuumpressure 857 (corresponding to the latest sensor reading provided byvacuum pressure sensor 659) and vacuum pressure set point 656. Usingfirst loop error 880, first PID controller 868 is then configured tocompute both the derivative and the integral of first loop error 880with respect to time. The first PID controller 868 further computes aproportional term using the first loop error. Based on suchcomputations, PID controller 868 is configured to provide a firstvoltage 886 as output, which corresponds to a control value forminimizing the difference between the current vacuum pressure 857 andthe vacuum pressure set point 656.

Vacuum generation system 800 further comprises a second feedback loop820 having a second, override PID controller 866 that takes overrideloop error 884 as input, where override loop error 884 corresponds tothe difference between the supply air pressure set point 882 (asdetermined or provided by the user) and the current supply air pressure851. The current supply air pressure 851 corresponds to the latestsensor reading that is provided by supply air pressure sensor 860. Incertain embodiments, the supply air pressure set point 882 may beprovided within the range of 0-60 psig (e.g., corresponding to themonotonic region of vacuum generator 650). For example, the supply airpressure set point 882 may be set to a maximum supply air pressure(e.g., 60 psig, which may be unchanging (e.g., constant) or staticduring use) corresponding to a maximum vacuum pressure of the monotonicregion of vacuum generator 650. As described further below, limiting therange of the supply air pressure helps with ensuring stability of vacuumgeneration system 800.

Using override loop error 884, override PID controller 866 is thenconfigured to compute both the derivative and the integral of overrideloop error 884 with respect to time. The override PID controller 866further computes a proportional term using the override loop error 884.Based on such computations, override PID controller 866 is configured todetermine a second voltage 890 as output, which corresponds to a controlvalue for minimizing the difference between the current supply airpressure 851 and supply air pressure set point 882.

The first voltage 886 calculated by first PID controller 868 and thesecond voltage 890 calculated by override PID controller 866 arecompared by a minimum control effort analyzer 894 to determine a minimumvoltage 898, corresponding to the lower voltage level of the firstvoltage 886 and the second voltage 890. The minimum voltage 898 is thenprovided to proportional valve 652, which then sets the supply airpressure 851 based on the provided minimum voltage 898. As describedpreviously, vacuum generator 650 takes as input supply air, whosepressure (i.e., supply air pressure 851) is set by a proportional valve652, and creates vacuum with a certain vacuum pressure 857. In someembodiments, the integral value calculated by the loop with the lowervoltage level (i.e., the integral value determined by the first PIDcontroller 868 if the first voltage 886 is smaller than the secondvoltage 890 or the integral value determined by the override PIDcontroller 866 if the second voltage 890 is smaller than the firstvoltage 886) is provided to both the first PID controller 868 and theoverride PID controller 866 for use as the integral value in the nextvoltage calculation.

Using both first PID controller 868 and override PID controller 866allows vacuum generation system 800 to control vacuum pressure 857 bylimiting the range of supply air pressure 851 that is provided into thevacuum generator 650, thereby eliminating or reducing the likelihood ofvacuum generator 650 operating in its decreasing and non-monotonicrange. More specifically, the first PID loop, involving the first PIDcontroller 868, uses the vacuum pressure feedback, which includes thecurrent vacuum pressure 857 (e.g., primary parameter), and the desiredvacuum pressure set point 656 to output first voltage 886. On the otherhand, the override PID loop, involving the override PID controller 866,takes supply air pressure set point 882 and supply air pressurefeedback, which includes the current supply air pressure 851 (e.g., thesecondary parameter), to output second voltage 890.

In operation, in certain embodiments, the first feedback loop 810generally controls the vacuum generation system 800 when the supply airpressure 851 is below the supply air pressure set point 882 (e.g., 60psig). In such an example, the first voltage 886 generated by the firstPID controller 868 is lower than the second voltage 890 generated by theoverride PID controller 866 and is provided to proportional valve 652 tocontrol supply air pressure 851. However, when the supply air pressure851 approaches, equals, or exceeds the supply air pressure set point882, the second feedback loop 820 takes control of the vacuum generationsystem 800 by providing a second voltage 890, which is at that pointlower than the first voltage 886, to proportional valve 652. The secondfeedback loop 820 thus acts to monitor the supply air pressure 851 andtakes over control of the system 800 from the first feedback loop 810when the supply air pressure 851 approaches, equals, or exceeds thesupply air pressure set point 882, thus preventing the vacuum generationsystem 800 from entering the non-monotonic region or minimizing theamount of time the vacuum generation system 800 operates in thenon-monotonic region. Further, by utilizing the minimum control effortanalyzer 984, there is a seamless transition between control by thefirst feedback loop 810 and the second feedback loop 820.

Accordingly, in certain embodiments, due to transient effects, thevacuum generation system 800 may enter the non-monotonic region as aresult of the supply air pressure 851 exceeding the supply air pressureset point 882. In such situations, the second feedback loop 820 becomesthe active controller to drive the vacuum generation system 800 backtowards the supply air pressure set point 882, thereby making thepresence of the vacuum generation system 800 in the non-monotonic regiontemporary as opposed to permanent. In other words, the second voltage890 may be larger than the first voltage 886 for a short period of timein the non-monotonic region, but the override PID controller 866 willquickly decrease the second voltage 890 such that the second feedbackloop 820 assumes control and the proportional valve 652 will decreasethe supply air pressure 851 until it reaches the supply air pressure setpoint 882.

In other words, using both the first PID controller 868 and the overridePID controller 866, as described herein, allows vacuum generation system800 to control the operating range of a secondary parameter (e.g.,supply air pressure), based on which vacuum generation system 800 isable to avoid entering the decreasing or non-monotonic region of vacuumgenerator 650. Preventing vacuum generation system 800 from experiencingaccidental suction and entering the decreasing and non-monotonic regionof vacuum generator 650 improves performance responsiveness (e.g.,performance speed) of vacuum generation system 800 because the systemdoes not need to recover from instability.

Further note that the override PID controller design described hereincan be implemented in various other systems that, similar to vacuumgeneration system 800, work with a primary parameter (e.g., vacuumpressure) and a secondary parameter (e.g., supply air pressure), suchthat the primary parameter is calculated based on the secondaryparameter. By implementing the override PID controller design describedherein in such systems, the secondary parameter can be controlled basedon a minimum output (e.g., voltage value) that corresponds to the lowerof a first output (e.g., first voltage 886) and a second output (e.g.,second voltage 890), where the first output is calculated based on thecurrent primary parameter (e.g., vacuum pressure 857) and the primaryparameter set point (e.g., vacuum pressure set point 656) and the secondoutput (e.g., second voltage 890) is calculated based on the currentsecondary parameter (e.g., supply air pressure 851) and a secondaryparameter set point (e.g., supply air pressure set point 882).

In other words, any system that operates with primary and secondaryparameters, such as above, can benefit from the override PID controllerdesign described herein.

Also note that the ranges provided here for the inputs, outputs, or setpoints are exemplary. In other words, these ranges may be tweaked basedon manufacturing and/or user preferences as well as the type andcharacteristics of the components of the system. For example, a vacuumgeneration system may use a vacuum generator that does not enter itsnon-monotonic operating range until the supply air pressure reaches 90psig. In such a case, the range for the supply air pressure set pointmay be defined as 0-90 psig. In another example, a different type ofvacuum generator may enter its non-monotonic operating range when thesupply air pressure reaches 40 psig. In such a case, the range for thesupply air pressure set point may be defined as 0-40 psig. Other rangesfor inputs, outputs, or set points may similarly be changed depending onthe factors described above as well as other factors, as one of ordinaryskill in the art appreciates.

Also note that although two feedback loops are described above, morethan two feedback loops may be used in combination. For example, thevacuum generation system 800 may further comprise a third feedback loophaving a second override PID controller configured to take as input athird loop error corresponding to a difference between the currentsupply air pressure and a second supply air pressure set point (asdetermined or provided by the user). In certain embodiments, the secondsupply air pressure set point may be set to a minimum supply airpressure (e.g., which may be unchanging during use) corresponding to aminimum vacuum pressure of the monotonic region of the vacuum generator650. Using the third loop error, the second override PID controller maybe configured to determine a third voltage as output, which may then becompared against the first voltage 886 before the minimum control effortanalyzer 894 or against the minimum voltage 898 after the minimumcontrol effort analyzer 894 by a maximum control effort analyzer. Uponcomparison, the higher (e.g., maximum) of the comparted voltage levelsmay then be provided by the maximum control effort analyzer as output.Accordingly, a minimum operating range for the vacuum generation system800 may be established utilizing the same system structure but includingan additional feedback loop. In some embodiments, using a secondoverride loop may not require using a minimum output. For example, aminimum comparator may be used between the vacuum pressure and firstoverride loop, and a maximum comparator may be used between the resultof the minimum comparator and the output of the second override loop. Insome embodiments, the same sensors may be used. For example, when usingsupply pressure, a second override loop may be used to prevent supplyair pressure from going too low or too high.

There are a variety of ways vacuum generation system 800 may beimplemented, as one of ordinary skill in the art appreciates. Forexample, in certain embodiments, all components of the system may beconfigured to communicate digitally. In such embodiments, the use ofdigital-to-analog converters (DACs) or analog-to-digital converters(ADCs) may not be necessary. In certain other embodiments, allcomponents of the system may be analog. Similarly, in such embodiments,the use of digital-to-analog converters (DACs) or analog-to-digitalconverters (ADCs) may not be necessary. In certain other embodiments,some of the components of the system may be analog and some others maybe digital. For example, in certain other embodiments, first PIDcontroller 868, override PID controller 866, and the minimum controleffort analyzer 894 may correspond to software instructions that can beretrieved from a memory and then executed by a processor. In suchembodiments, because any output provided by the processor is digital,digital-to-analog converters (DACs) may be used to allow the processorto communicate with some of the analog components (e.g., a drivercircuit, proportional valve 652, etc.) of the system. Similarly, ADCsmay be used by certain components, such as supply air pressure sensor860 and vacuum pressure sensor 659 to communicate with the processor.

FIG. 9 illustrates vacuum generation system 900, which corresponds to anexample implementation of vacuum generation system 800. Vacuumgeneration system 900 includes a processor and a memory (collectivelyreferred to as “processor and memory 980”) to perform calculations ofthe first loop error 880 and the override loop error 884 as well as thePID calculations of the first PID controller 868 and the override PIDcontroller 866. The processor and memory 980 may also calculate theminimum voltage 898 corresponding to the lower of the first voltage 886and the second voltage 890. The processor is configured to retrieve andexecute programming instructions stored in the memory. The processor mayinclude a single CPU (central processing unit), multiple CPUs, a singleCPU having multiple processing cores, and the like. The memory may beone or more of a readily available memory, such as random access memory(RAM), read only memory (ROM), floppy disk, hard disk, solid state,flash memory, magnetic memory, or any other form of digital storage,local or remote. In certain embodiments, the memory includesinstructions, which when executed by the processor, performs thecalculations of the first loop error 880 and the override loop error884, the PID calculations of the first PID controller 868 and theoverride PID controller 866 as well as the minimum voltage 898. Incertain embodiments, the processor and memory 980 may be the mainprocessor and memory of surgical console 101, which may implement orinclude vacuum generation system 900.

As described above, one or more DACs and ADCs may be used for thecommunication between the processor and other components in the system.For example, the processor may indicate the calculated minimum voltagevalue to an interface 862, which may include a DAC as well as a drivercircuit. When the driver circuit receives an analog signal from the DACthat indicates the calculated minimum voltage value, the driver circuitprovides the corresponding amount of voltage to proportional valve 652.The use of a DAC and a driver circuit is merely exemplary. Other typesof interfaces may be used instead, as one of ordinary skill in the artappreciates. Further, in certain embodiments, supply air pressure sensor860 and vacuum pressure sensor 659 are analog components. As such,supply air pressure sensor 860 may use interface 870, which may be anADC, to communicate with the processor. Similarly, vacuum pressuresensor 659 may use interface 864, which may be an ADC, to communicatewith the processor.

FIG. 10 illustrates example operations 1000 of a vacuum generationsystem, according to some embodiments. In certain embodiments,operations 1000 are performed by the vacuum generation system 800 ofFIG. 8. The process 1000 are described herein with reference to FIG. 8and its components.

At 1002, a vacuum generation system (e.g., vacuum generation system 800)receives a vacuum pressure sensor reading from a vacuum pressure sensor(e.g., vacuum pressure sensor 659).

At 1004, the vacuum generation system calculates a first loop error(e.g., first loop error 880) between the vacuum pressure sensor reading(e.g., vacuum pressure sensor 659) and a vacuum pressure set point(e.g., vacuum pressure set point 656).

At 1006, the vacuum generation system calculates (e.g., using a firstPID controller 868) a first voltage level for controlling a proportionalvalve (e.g., proportional valve 652) based on the first loop error.

At 1008, the vacuum generation system receives a supply air pressuresensor reading from a supply air pressure sensor (e.g., supply airpressure sensor 860).

At 1010, the vacuum generation system calculates an override loop error(e.g., override error 884) between the supply air pressure sensorreading and the supply air pressure set point 882.

At 1012, the vacuum generation system calculates (e.g., using a secondPID controller (e.g., override PID controller 866)) a second voltagelevel or value for controlling a proportional valve (e.g., proportionalvalve 652), the second voltage value being based on the override looperror.

At 1014, the vacuum generation system determines a minimum voltage levelcorresponding to the lower of the first and second voltage levels. Theminimum voltage level is associated with an input into the proportionalvalve.

At 1016, the vacuum generation system provides the minimum voltage levelto the proportional valve.

At 1018, the vacuum generation system provides, using the proportionalvalve, supply air pressure to a vacuum generator (e.g., vacuum generator650) based on the minimum voltage level.

At 1020, the vacuum generation system provides, using the vacuumgenerator, vacuum pressure based on the supply air pressure to asurgical tool (e.g., tool 103 of FIG. 1). In some embodiments, theintegral value calculated by the loop with the lower voltage level(i.e., the integral value determined by the first PID controller 868 ifthe first voltage 886 is smaller than the second voltage 890 or theintegral value determined by the override PID controller 866 if thesecond voltage 890 is smaller than the first voltage 886) is provided toboth the first PID controller 868 and the override PID controller 866for use as the integral value in the next voltage calculation.

The foregoing description is provided to enable any person skilled inthe art to practice the various embodiments described herein. Variousmodifications to these embodiments will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other embodiments. Thus, the claims are not intended to belimited to the embodiments shown herein, but are to be accorded the fullscope consistent with the language of the claims.

Example Embodiments

Embodiment 1: A method of controlling vacuum pressure in a vacuumgeneration system, the method comprising: receiving a first parametersensor reading from a first parameter sensor; calculating a first errorbetween the first parameter sensor reading and a first parameter setpoint; determining a first voltage value based on the calculated firsterror; receiving a secondary parameter sensor reading from a secondaryparameter sensor; calculating a second error between the secondaryparameter sensor reading and a secondary parameter set point;determining a second voltage value based on the calculated second error;determining a lower value of the first and second voltage values;providing an input with the lower value to an actuator; providing, usingthe actuator, the secondary parameter to a device based on the input.

Embodiment 2: A method of controlling vacuum pressure in a vacuumgeneration system, the method comprising: receiving a first parametersensor reading from a first parameter sensor; calculating a first errorbetween the first parameter sensor reading and a first parameter setpoint; calculating, using a first proportional-integral-derivative (PID)controller, a first value associated with a first input into an actuatorbased on the first error; receiving a secondary parameter sensor readingfrom a secondary parameter sensor; calculating a second error betweenthe secondary parameter sensor reading and a secondary parameter setpoint; calculating, using a second PID controller, a second valueassociated with a second input into the actuator based on the seconderror; determining a lower value of the first and second values;providing the first or second input with the lower value to theactuator; providing, using the actuator, the secondary parameter to adevice based on the provided input; and providing, using the device, thefirst parameter based on the secondary parameter to a tool.

Embodiment 3: The method of Embodiment 2 described above, furtherincluding: receiving a third parameter sensor reading from a thirdparameter sensor; calculating a third error between the third parametersensor reading and a third parameter set point; calculating, using athird PID controller, a third value associated with a third input intothe actuator based on the third error; determining a lowest value of thefirst, second, and third values; and providing the first, second, orthird input with the lowest value to the actuator.

Embodiment 4: The method of Embodiment 3 described above, wherein thethird parameter is a temperature limit that prevents overheating of aproportional valve by limiting a voltage provided to the proportionalvalve.

What is claimed is:
 1. A method of controlling vacuum pressure in avacuum generation system, the method comprising: receiving a vacuumpressure sensor reading from a vacuum pressure sensor; calculating afirst error between the vacuum pressure sensor reading and a vacuumpressure set point; calculating a first voltage level for controlling aproportional valve based on the first error; receiving a supply airpressure sensor reading from a supply air pressure sensor; calculating asecond error between the supply air pressure sensor reading and a supplyair pressure set point; calculating a second voltage level forcontrolling a proportional valve based on the second error; determininga lower of the first and second voltage levels; providing an inputvoltage level corresponding to the lower voltage level to theproportional valve; causing, using the proportional valve, supply airpressure to be provided to a vacuum generator based on the lower voltagelevel; and providing, using the vacuum generator, vacuum pressure basedon the supply air pressure to a surgical tool.
 2. The method of claim 1,wherein calculating the first voltage level is performed by a firstproportional-integral-derivative (PID) controller and whereincalculating the second voltage level is performed by a second PIDcontroller.
 3. The method of claim 2, wherein the first PID controllerdetermines a first integral value and wherein the second PID controllerdetermines a second integral value and wherein the integral valuedetermined by the PID controller with the lower of the first or secondvoltage level is provided to both the first PID controller and thesecond PID controller for use as the integral value in a subsequentvoltage determination.
 4. The method of claim 1, wherein calculating thesecond voltage level based on the second error comprises limiting thesupply air pressure set point to a range that corresponds to a monotonicoperating range of the vacuum generator.
 5. The method of claim 4,wherein the supply air pressure set point is a constant, and wherein thesupply air pressure set point is set equal to a maximum supply airpressure within the range.
 6. The method of claim 3, wherein the firstPID controller is a primary driver of the vacuum generation system anddrives the vacuum generation system when the first voltage level islower than the second voltage level.
 7. The method of claim 6, whereinthe second PID controller drives the vacuum generation system when thesecond voltage level is less than the first voltage level.
 8. A vacuumgeneration system, comprising: a first proportional-integral-derivative(PID) controller, configured to: receive a first error between a vacuumpressure sensor reading associated with a vacuum generator and a vacuumpressure set point; and calculate a first voltage level based on thefirst error; a second PID controller, configured to: receive a seconderror between a supply air pressure sensor reading and a supply airpressure set point; and calculate a second voltage level based on thesecond error; a minimum control effort analyzer, configured to:determine a lower voltage level between the first and the second voltagelevels; and relay the lower voltage level to a proportional valve; theproportional valve, configured to: cause supply air pressure to beprovided to a vacuum generator based on the lower voltage level; and thevacuum generator, configured to: provide vacuum pressure based on thesupply air pressure to a surgical tool.
 9. The vacuum generation systemof claim 8, further comprising: a vacuum pressure sensor, configured toprovide the vacuum pressure sensor reading; and a supply air pressuresensor, configured to provide the supply air pressure sensor reading.10. The vacuum generation system of claim 8, wherein the second PIDcontroller controls the proportional valve when the supply air pressureequals or exceeds a supply air pressure set point of the second PIDcontroller.
 11. The vacuum generation system of claim 10, wherein thesupply air pressure set point may be between approximately 40 to 60psig.
 12. A vacuum generation system, comprising: a memory comprisingexecutable instructions; a processor in data communication with memoryand configured to execute the instructions, which configured theprocessor to; receive a first error between a vacuum pressure sensorreading associated with a vacuum generator and a vacuum pressure setpoint; calculate a first voltage level based on the first error; receivea second error between a supply air pressure sensor reading and a supplyair pressure set point; calculate a second voltage level based on thesecond error; cause the lower voltage level between the first and secondvoltage levels to be provided to a proportional valve; the proportionalvalve, configured to: cause supply air pressure to be provided to avacuum generator based on the lower voltage level; the vacuum generator,configured to: provide vacuum pressure based on the supply air pressureto a surgical tool.
 13. The vacuum generation system of claim 12,further comprising: a vacuum pressure sensor, configured to provide thevacuum pressure sensor reading; and a supply air pressure sensor,configured to provide the supply air pressure sensor reading.
 14. Thevacuum generation system of claim 12, wherein calculating the secondvoltage level based on the second error comprises limiting the supplyair pressure set point to a range that corresponds to a monotonicoperating range of the vacuum generator.
 15. The vacuum generationsystem of claim 14, wherein calculating the second voltage level basedon the second error comprises limiting the supply air pressure set pointto a range of 0-60 psig (pounds per square inch gauge).